Two helicopters are on their way to pick up an ill 80-year-old man from a cruise ship in the Tasman Sea.

The helicopters were sent from Te Anau to carry out the medical evacuation.

It was usual to use two helicopters for long distance evacuations, Rescue Coordination Centre New Zealand spokeswoman Sophie Hazelhurst said.

The helicopters were expected to rendezvous with the cruise liner Silver Shadow about now.

The man had suffered "some sort of medical event" and would be winched to a helicopter and flown to either Southland or Dunedin Hospital.

The Silver Shadow was heading from Australia to Milford Sound and was 125 nautical miles (232km) west of Milford Sound.